Process of producing all skin rayon



United ates ihatcnt 2,343,453 Patented July 1, 19 58 y til rnocnss or Pnonucnvo ALL sun navorv No Drawing. Application June 29, USS Serial No. 519,066

Claims. (Cl. Ill-=54) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

in the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a Xanthate by treatment with carbon disulfide. The cellulose Xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aque ous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to Washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent dilferences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stifi.

It has now been discovered that the presence of small amounts of phenylenediamine or diaminobenzene in viscose results in the production of shaped bodies of regen erated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of the phenylenediamine is maintained with certain limits and the composition of the spinning bath is maintained within certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

Any of the phenylenediamines are satisfactory for the purposes of this invention, that is, the 0-, mand p-forms (1,2-, 1,3- and 1,4-diaminobenzene). The m-phenylene- -diarnine is preferred because of the toxicity of the oand p-forms. The modifier may be conveniently added in the form of a solution in water or in a caustic soda solution.

The amount of phenylenediamine which is incorporated in the viscose must be at least about 0.4% by Weight of the cellulose in the viscose and may vary up to about 3%, preferably, the amount varies from 0.5% to 2%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts afiect adversely the physical properties of the products. Amounts Within, the preferred range are most efiective in enhancing the characteristics and properties of the products. The phenylenediamine may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose While it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The phenylenediamine is preferably added after the cellulose Xanthate has been dissolved in the canstic solution and prior to filtration.

The viscose may contain from about 6% to about 8% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose containing the small amount of phenylenediamine, may have a salt test above about 7 and preferably above about 8 at the time of spining or extrusion.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained Within a well defined range. The presence of the phenylenediarnine in the viscose combined with these limited spinnning baths results in the production of yarns of improved properties such as high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath containing from about 10% to about 25% sodium sulfate and from about 3% to about 15% zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and replace some of the Zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about C., preferably between about 45 C. and about 70 C. As is Well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spining bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is Well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For coma skin and core.

There is a maximum acid concentration for any specific viscose composition beyondwhich the neutralization is sufficiently rapid to produce filaments having skin and core. centration of the spinning baths which are satisfactory for the production of the all skin products from a 7% cellulose, 6% caustic-viscose and containing phenylenediamine lies between about and about 7.7% to 7.8%. The acid concentration may be increased as the amount of the modifier is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of modifier and the concentration of caustic in theviscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of the phenylenediamine'is increased beyond about 3% While other conditions are maintained constant. 7 ing about 7% cellulose, about 6.5% caustic soda, about 35 (based on the weight of the cellulose) carbon disulfide, and 1% (based on the weight of cellulose) of phenylenediamine and having a salt test of about 9 when extruded intospinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid not more than about 7.6% results in the production of all' skin filaments Lesser amounts of sulfuric acid 'may be employed. Greater amounts of sulfuric acid result in the productionof products having skin and core. A lowering of the amount of the modifier, the lowering the caustic acid content or the lowering of the salt test of the viscosereduces the maximum permissible acid concentration for the production of all skin filaments. The maximum concentration of acid which is permissible for the production of all skin products is about 9%. 7

The presence of the phenylenediamine in the viscose retards the coagulation and, therefore, the amount of derivative employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and i at aspinning speed of about 5 0 meters per-minute,

the modifier is employed in amounts within the lower portion ofthe range, for example, about 1%. termination of the specific maximum'and optimum con- For example, in general, the acid coni For example, a viscose contain- The de- 5 For any specific viscose cornposition, the acid concentration of the spinning bathmust 1 b e-maintained above the slubbing point and below thepoint at which the neutralization of the caustic of the viscose is sufficiently rapid to form a filament having bleaching and the like.

the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to.

about 5% sodium sulfate with or without small amounts. of zinc sulfate if regeneration has not previously been completed. V

The treatment following the final regenerating bath, orthe stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing st o t e application of a finishing or plasticizing matoria drying before or after collecting, or may include other desired and conventional steps such as tion will be dictated by the specific type of shaped body and the proposed use thereof. j i

Regenerated cellulose filaments prepared from viscose containing the small amounts ofphenylenediamine The treatment after regenera-.

have a smooth 'or non-crenulated surface and. consist.

entirely of'skin. Because of the uniformity of structure throughout the filament, the swelling and stainingchare acteristics are uniform throughout the cross-section of the filament.

Filaments produced pursuant to this in vention and consisting entirely of skin have a high. toughness and a greater flexing life than filamentsas produced according to prior methods which may be" attributed by the uniformity in skin structure through- Although the twisting of conventional filaments, as in the production of tire cord, results in out the filament.

an appreciable loss of tensile strength, there is appreance characteristics and have a high flex-life.

Suchfilaments are highly satisfactory for the production of cords for the reinforcement of rubber products such. as pneu-J' matic tire casings, .but the filaments are notrestricted 1 to such uses and may be used for other textile applications; I The invention may be illustrated by reference to thepreparation 'of regenerated cellulose filaments from a" viscose modified with m-phenylenediamine (1,3-diamino benzene) and con .g about 7% cellulose, about 6.5%-

caustic soda, and aving a total carbon disulfi'de con 1 for about /2 hour.

the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath From the initial spinning bath, the

I filaments may be passed through a hot aqueous bath The precise amount of stretching will be dependent upon V the desired tenacity and other properties and the spesulfate.

tent of about based on the weight of thec ellulose.

The viscose. solutions were prepared by xanthating alkali: cellulose by'the introduction of 35% carbondisulfidebased on the. weight of the celluloseand churningfor about 2 /2 hours.

The cellulose xanthate was then dissolved in caustic soda solution. The desired-amount of m-phenylenediamine was added to the solution and mixed ripen for about 30 hours at 18 C.

' Example 1 The viscose was then allowed to Approximately 0.5% (based'on the weight of the cellu lose) m-phenylenediamine was added to and incorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 9. The viscose was extruded through a spinneret to form a 200 denier, 120 filament yarn'at a rate of about 43 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about C. andcontained 7.3% sulfuric acid, 7.4% zinc sulfate and 16.5% sodium ing through a hot Water bath at 98 C. The yarn was collected ina spinning box," washed free of acids and salts and dried.

cific type of product being produced. It is to beiunderstood that the; invention is not restricted to the produc-.

tion of filaments and yarns but it is also applicable to other shapedbodies such as sheets, films, tubes and The individual filaments have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e. 1500 X). The filaments of a control yarn spun with the same viscose but without the addition of the modified agent and spun.

under the same conditions, exhibit a very irregular and The yarn was stretched about 74% while passthe balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 2 To a viscose as described above, there was added 1% m-phenylenediamine. The viscose had a salt test of 9 and was spun into a 200 denier, 120 filament yarn by extrusion into a spinning bath containing 7.3% sulfuric acid, 7.5% zinc sulfate and 16.7% sodium sulfate. bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were subsequently passed through a hot water bath at 98 C. and stretched about 82%. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin while the control filaments have a very irregular and serrated surface and consist of about 80% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 3 To a viscose solution as described above, there was added 1% rn-phenylenediamine. The viscose had a salt test of 9 and was spun into a 327 denier, 40 filament cord by extrusion into a bath containing 7.3% sulfuric acid, 7.5% zinc sulfate and 17% sodium sulfate. The bath was maintained at a temperature of 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at about 95 C. and the filaments were stretched approximately 57% while passing through the hot water. The cord was washed free of acid and salts by treatment with water at about 98 C. on thread-advancing reels, dried and collected on cones.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no modifier in that they have a smooth, non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of about 80% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 4 As a control for the foregoing examples, a viscose solufion, prepared as described above, having a salt test of 9 was spun into a 210 denier, 120 filament yarn by extrusion into a bath containg 7.4% sulfuric acid, 7.3% zinc sulfate and 16% sodium sulfate. The bath was maintained at a temperature of about 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at a temperature of about 98 C.

and the filaments were stretched 82% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments have a very irregular and serrated surface and consist of about 80% skin and the balance core with a sharp line of demarkation between the skin and the core. Other characteristics are set forth in the table which follows:

Although the tenacity and elongation are the only Theproperties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tenacity and elongation, however, the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about to about for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The phenylenediamine may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The modifying agent may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the phenylenediamine at the time of spinning.

If desired, small amounts of the modifying agent may be added to the spinning bath. Since oand m-phenylenediamine are water-soluble, some of the modifier will be leached from the filaments and will be present in the bath. Although p-phenylenediamine is sparingly soluble, the small amounts required would be within the solubility limits and will also be leached from the filaments.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60 and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing from about 0.4% to about 3%, based on the weight of the cellulose, of a phenylenediamine into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%.

2. The step in the method as defined in claim 1 wherein the phenylenediamine is m-phenylenediamine.

3. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin the steps which comprise adding to and incor orating in viscose from about 0.5% to about 2%, based on the weight of the cellulose, of a phenylenediamine and extruding the viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate, and sulfuric acid, the sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 9%.

4. In a' method' ofproducing shaped-bodies of regenw erated cellulose consisting substantially entirely of skin",

the steps which comprise adding to and incorporating in not lower than about 9 and extruding the viscose into an aqueous spinning bath containing from about 16% to 20% sodium sulfate, from about 4% to 9% zinc sulfate and sulfuric acid, the sulfuric acid content'of the spinning bath exceeding the slubbi ng point but not exceeding about;

5. The steps in the method as defined in claim 4 where in the phenylenediamineiis m-phenylenediamine.

' I References Ci tedin the file o fthi s patent UNITED S TATESPATENTS Davis Feb. 23, 1943 Schlosser Apr. 17,1945 Cox" Dec. 26, 1950 MacLaurin Apr. 22, 1952 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEP WHICH COMPRISES EXTRUDING VISCOSE CONTAINING FROM ABOUT 0.4% TO ABOUT 3%, BASED ON THE WEIGHT OF THE CELLULOSE, OF A PHENYLENEDIAMINE INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO 25% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINC SULFATE AND SULFURIC ACID, THE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 9%. 